Method of repairing a hydrogenerator

ABSTRACT

A method for repairing an electric generator having a rotor that rotates about a vertical axis, the rotor including a spider having a number of spider arms extending radially away from the axis, and a rim surrounding the spider. The weight of the rim is normally carried at least in part by rim support ledges of the spider arms. The method for repair includes supporting the rim from the top of the spider and thereby relieving some or all of the weight of the rim being supported by the rim support ledges

This application claims priority from related provisional application62/948,021.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method of repairing ahydrogenerator.

BACKGROUND OF THE DISCLOSURE

Background information is for informational purposes only and does notnecessarily admit that subsequently mentioned information andpublications are prior art.

Hydroelectric power comes from flowing water, for example, winter andspring runoff from mountain streams and clear lakes. Water, when it isfalling by the force of gravity, can be used to turn turbines andgenerators that produce electricity.

At facilities called hydroelectric powerplants, hydropower is generated.Some powerplants are located on rivers, streams, and canals, but for areliable water supply, dams are needed. Dams store water for laterrelease for such purposes as irrigation, domestic and industrial use,and power generation. The reservoir acts much like a battery, storingwater to be released as needed to generate power.

FIG. 1 illustrates a hydropower plant that includes an upper body ofwater 10 feeding a turbine 1 through a pressure line 20 via a shutoffelement 30. The turbine 1 drives a generator 40 that generateselectricity. The turbine 1 and the electric generator 40 together form ahydrogenerator (hydroelectric generator) 70.

As shown in FIG. 2, a dam creates a reservoir forming the upper body ofwater 10. The reservoir has a “head” or height from which water flows. Apipe (penstock) carries the water from the reservoir to thehydrogenerator 70. The hydrogenerator 70 shown in FIG. 2 is a verticalhydro generator designed around a vertically mounted shaft assembly.Attached to the upper portion of the shaft assembly is a rotor 100 (seeFIG. 3) of the generator 40. Attached to the lower end of the shaft isthe turbine 1. The turbine 1 has turbine blades driven by thefast-moving water from the penstock, something like a pinwheel in thewind. The turbine 1 drives the rotor 100 within a stator of the electricgenerator 70 to generate electricity.

FIG. 3 shows a rotor 100 of a typical electric generator 40, and FIG. 3Ashows a cross-section of the circled portion of the rotor 100 in FIG. 3.The rotor 100 includes a shaft 102 and a spider 103 attached to theshaft 102. The spider 103 supports a rim 108 surrounding the shaft 102.The rim 108 carries a number of poles 110 spaced along the outercircumference of the rim 108. When the poles 110 pass by poles in thestator during rotation of the rotor 100, the electric generator 70generates electricity.

The illustrated spider 103 is a welded steel structure having six spiderarms 104 with vertical posts 105 at their ends that support the rim 108.The rim 108 is a ring of laminated steel segments held together by solidsteel end plates 109 at the top and bottom, and clamped together bybolts 130 (see FIG. 6) passing through the end plates and laminations.The rotor poles 110 in turn are supported by the rim 108 both radially,usually by dovetails, and axially by the rim 108.

The weight of the rotor 100 and the rim 108 are supported on thevertical posts 105 of the spider arms 104. Each vertical post 105 isprovided with a rim support ledge 106 machined in the base of thevertical post. FIG. 3B shows a close-up view of a rim support ledge 106machined in the base of the vertical post 105. In general, the rim 108is supported on the rim support ledges 106, and is mounted on the spiderarms 104 by a friction fit.

A common problem that occurs in the operation of the electric generator40 is that wear occurs at the rim support ledge 106 generally due tofriction between the rim 108 and the rim support ledge 106. Because ofdifferent operational forces and other factors, the rim 108 may movewith respect to the rim support ledge 106, which can ultimately lead todamage, such as the fracture 112 of the rim support ledge 106illustrated in FIG. 3B.

Examples of operational forces that may cause the rim 108 to move withrespect to one or more of the rim support ledges 106 include highfrequency forces that may occur once or twice with each revolution ofthe rotor 100:

eccentricity (out of roundness) of the rotor 100; and

unbalanced magnetic forces that can distort the rim 108.

An unbalanced magnetic pole vector V on the rotor 100 is shown in FIG.4. The clearance 114 at the top of FIG. 4 is shown as the clearance withthe rim 108 concentric. The eccentricity 116 at the bottom of FIG. 4 isshown as clearance with the rim 108 eccentric. The magnetic forcesdistort the rim 108 during operation whereby, because of the rim'sconstruction in layers, fretting or other wear occurs which ultimatelyleads to the failure of some part of the rotor structure which then mustbe repaired. The lateral flexibility of the spider arms 104 plus theloss of frictional interference between the rim 108 and the spider arms104 permits the rim 108 to slide on the ledges 106 at each start, andalso once per revolution, when exposed to an unbalanced magnetic pole.It is very difficult if not impossible to build a hydrogenerator whichdoes not have an unbalance magnetic pole. Even the slightest unbalancewill cause the components of the rotor to move with respect to oneanother and cause fretting if not other wear on the rotor.

Examples of operational forces that may cause the rim 108 to move withrespect to one or more of the rim support ledges 106 include low cycleforces that occur with start/stop of the hydrogenerator 70 or arise fromtransient operating conditions:

radial expansion of the rim 108 caused by rotation of the rim 108;

differential radial expansion of the rim 108 caused by the rim 108heating more than the spider 103 during operation;

stopping and cooling of the rim 108 when the hydrogenerator 70 is shutdown; and

overspeed/runaway conditions, out-of-phase synchronizations, shortcircuits, and transient torque spikes.

FIG. 5 shows the force 118 of the dead weight of the rim 108 and thepoles 110 pulling down on the spider arms 104. FIG. 5A shows thetraction (friction) force 120 from sliding, which forces combine tocause wear during operation. The dead weight of the rim 108 and thepoles 110 will act upon components of the hydroelectric generator 70. Ateach start and stop of the hydroelectric generator 70 there will be acentrifugal force on the generator rim 108, thereby causing thecomponents thereof to move with respect to one another. The movement ofthe components with respect to one another will cause or contribute incausing the fretting or other damage to the components of the rotor 100,which will accelerate damage and the appearance of cracks in thestructure of the rotor 100.

In general, hydrogenerators often experience fatigue cracking of therotor rim support ledges. The rim support ledges are where fatigue andwear caused by the relative movement of the rim can occur. The wear canproduce cracking and eventually even a complete fracture or breaking offof a rim support ledge. Since the ledges provide support for the rim,breakage of these ledges could result in significant damage to the rotoras a whole and individual components thereof, as well as any adjacentportions of the hydrogenerator.

The most common approaches to repair damaged rim support ledges are toeither remove and then replace or refurbish the rim, or to providesupplemental supports beneath the rim or in the rim vent duct.Replacement or refurbishment is undesirable as it is very expensive,time-consuming, and requires complete removal or lifting of the rim.Supplemental supports beneath the rim are not usually able to carry thefull load of the rim and have poor resistance to fatigue. Supplementalsupports in the rim vent duct have the problems of not being applicableto all machines, difficulty in achieving load sharing, and having anindeterminate lifespan.

Thus, there is a need to provide a cost-effective repair method forhydrogenerators to extend the life span of a rim and spider of a rotorupon damage to the rim support ledges.

SUMMARY OF THE DISCLOSURE

Disclosed is a cost-effective repair method for hydrogenerators thatextends the life span of a rim and spider of a rotor upon damage to therim support ledges.

According to one possible embodiment, the repair method involves the rimbeing supported from the top of the spider posts instead of on the rimsupport ledges at the bottom of the spider posts. In general, supportstructures are attached to the tops of the spider posts to support therim from above and relieve the weight on the rim support ledges.

Embodiments of the support structures are thrust plates formed fromsteel having sufficient strength to support the rim while preservingductility and toughness for fatigue resistance. The thrust plates can beaffixed to the rim with sleeve bolts that thread to the rim clampingstuds. The sleeve bolts can be tightened periodically to compensate forwear of the thrust plates or to compensate for wear of wear platesplaced below the thrust plates.

The disclosed method for repair hangs the rim from the top of the spiderposts. The disclosed method has a number of advantages:

1. It replaces the rim ledge with a considerably stronger piece ofmaterial that is still ductile and has excellent fatigue resistance;

2. The support structures have a greatly reduced stress concentration atthe corner of the support as compared to the rim ledges;

3. The support structures control the friction between the rim supportand the spider post; and

4. The support structures reset the “fatigue cycles” counter to zerowith respect to support of the rim on the spider.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a possible hydropower plant;

FIG. 2 is a diagram of how a hydropower plant works;

FIGS. 3, 3A, and 3B show a typical geometry and failure location of arotor;

FIG. 4 shows an unbalanced magnetic pole vector on a rotor;

FIG. 5 shows the dead weight of the rim and the poles of a rotor;

FIGS. 6 and 7 show an embodiment of a thrust plate assembly for ahydrogenerator in place on the rotor shown in FIG. 3; and

FIG. 8 is a top view of the thrust plate of the thrust plate assemblyshown in FIG. 7.

DETAILED DESCRIPTION

FIG. 6 shows a thrust plate assembly having a thrust plate 122 used inan embodiment of the disclosed method for repairing the electricgenerator 40 shown in FIGS. 3 and 3B as having a fractured rim supportledge 106.

In general, in this embodiment a plurality of thrust plates 122 arelocated one at each of a corresponding spider arm 104. The thrust plates122 support the rim 108 from above on the spider arms 104. In otherwords, instead of the weight of the rim 108 resting solely on the rimsupport ledges 106, which one or more rim support ledges 106 are crackedor completely broken off, the weight of the rim 108 is supported by thethrust plates 122, such that the rim 108 is, in a sense, hanging fromthe thrust plates 122. The thrust plate 122 is spaced apart from the rim108 itself.

In the illustrated embodiment a wear plate or sacrificial plate 124 islocated in a recessed or stepped or shoulder portion 126 of the thrustplate 122 between the thrust plate 122 and the spider arm 104. A portionof the wear plate 124 may or may not extend so as to be in contact withthe top of the rim 108. The spacing of the thrust plate 122 a distancefrom the rim 108 prevents frictional contact between the thrust plate122 and the rim 108, and thus prevents wear. Instead, the wear plate124, which is lubricated with a solid lubricant, experiences frictionand wear.

As the wear plate 124 wears down, a sleeve bolt 128 can be tightenedperiodically to tighten the connection of the thrust plate 122. In thismanner, the life of the rotor 100 can be extended without extensiverepairs or replacement.

The following discusses the installation, design, and function of thethrust plate 122 in greater detail. It should be noted that all numbersand materials specifically listed for different parts and components andmeasurements thereof are strictly in accordance with at least onepossible embodiment and should not be understood as limiting theembodiments disclosed herein, as well as any reasonable variations ormodifications thereof.

FIG. 7 illustrates mounting of a thrust plate 122 on the rim 108adjacent to a spider arm vertical post 105, and FIG. 8 illustrates thefasteners fastening the thrust plate 122 on the rim top plate 109. Thethrust plates 122 can be 3″ (three inch) thick machined platesmanufactured from ASTM A829 SAE 4140 with a minimum yield strength of 70ksi, and a UTS not less than 118 ksi and a 40% reduction in area. Thisprovides strength while providing ductility and toughness for fatigueresistance. Each thrust plate 122 is affixed to the rim 108 with fivesleeve bolts 128 that thread to the rim clamping studs 130 (see FIG. 6),and two 1.25″ (one-and-one-quarter inch) alloy socket head cap screws132.

The sleeve bolts 128 are modeled for stress analysis as though a 2.75″(two- and three-quarters inch) Hex bolt with a suitable length ofunthreaded shank were cut off, bored and tapped with 1.75″-5 UNC insidethreads. The minimum tensile area of this configuration is slightlygreater than that of the original stud. The sleeve bolts 128 are madefrom commercial Grade 5 bolts, and thus will be at least as strong asthe rim studs 130. The length below the heads will be 3″ (three inches);then with the washers under the head, contact of the bottom of the shankwith the rim top plate 109 will be avoided.

The two 1.25″ (one-and-one-quarter inch) socket head cap screws 132 areused to resist localized bending due to the weight of the rim 108. Thedesign specification calls for a maximum of ⅓rd (one-third) of the rimweight to be carried by an individual thrust plate 122. This is slightlyover 33 tons for the illustrated rim, and though obviously could not becarried by all of the thrust plates 122, could conceivably be carried bysome of them. The rim top plate 109 must be drilled and tapped for theHelicoil thread insert corresponding to this thread.

Stress analysis (including the use of finite element models) and bothhigh-cycle fatigue analysis and low cycle fatigue analysis of the thrustplate, rim top plate in the vicinity of its attachment to the thrustplate, and the loading of the fasteners attaching the transfer plate tothe top of the rim were conducted. Stresses in the thrust plate, rim topplate in the vicinity of the attachment, and the loading of the sockethead cap screws were evaluated. Because the rim 108 now hangs from therim's top end plate 109, stresses in the top end plate are impacted.Also impacted are rim compression and rim studs, which in addition tothe clamping load now carry the weight of the rim in an area localizedto the thrust plate installation.

Evaluation of the thrust plate, rim, rim top plate and attachmentmethods under very conservative loading assumptions show that the repairmethod applied to the rotor 100 will be suitable for at least a 5 yearlife, and very likely for a considerable period beyond this ifnecessary. The conditions necessarily used for evaluation were found tobe conservative just as this report was being finalized. That is, it wasfound that the rotor rims were loose enough to be lifted off the spiderarm support ledges. This more certainly fixes the spider post deadweight loading at 1× the rim weight as a steady load (up-thrusting iseliminated). It was therefore concluded that the thrust plate repairwill be suitable for the service intended.

Further, in evaluating the application of the disclosed method forrepair to a specific hydrogenerator, it may not be known if it ispossible to lift the rim relative to the spider. This can result in asomewhat indeterminate loading situation. The rim would be leveled andthe thrust plates would be assembled to a cold rim. At that point thetransfer plates would be carrying little load. But as it is unclear howmuch load cracked ledges might bear (and clearly broken ledges wouldbear none), a complex load situation may be created. The loadingscenario may be based on solid rim support ledges. In order to bound thepossibilities of a lack of support from some of the ledges, the possibleload on an arm may be increased (for example, doubled).

It may be that the rim could be lifted from the support ledges. Thismakes it possible to control the loading scenario so that the spiderarms will carry only ⅙th (not ⅓rd) of the rim load each, as a steadyload. With careful friction control, then, the stress ranges due to rimmovement on the bearing surfaces may be lowered. As well, there will beno unloading of the rim weight as is posited in the low cycle fatiguescenario.

For some rotors, the spider is designed with uneven angular spacing ofthe rotor spider arms. Taken together. it appears that the intent was tomake the rim as close to “elastically solid” as possible. That is to saythat slipping between laminations, which would allow the rim to growcircumferentially leading to a loss of interference with the spider, isprevented (or attempted to be prevented) by high friction forces andclose fitting of the clamping bolts to the holes in the laminations.

In evaluating application of the disclosed method for repair to aspecific hydrogenerator, it may not be known if the hydrogenerator rimwas designed to “float” duration operation. Hydro generators of similarconstruction have been designed with floating rims; however, rimsutilizing an interference fit relative to the spider are more common.Regardless of the original design, it is accepted that the rim is nowfloating and likely has been for some time. That is, the rim outgrowsthe spider due to centrifugal forces and differential heating. This is asmall amount of movement and ideally occurs only once per start/stopcycle. This movement creates an alternating “push-pull” on the rimsupport ledges that is imposed on the steady state stresses due to thedead weight of the rim and poles. Thus, a low cycle fatigue situationwould likely exist even under ideal conditions just based on the designand construction, and the rim ledges should have been designed towithstand that scenario. Rim ledge cracking is ordinarily a high cyclefatigue problem caused by the normal imperfections of operation incombination with rim dead weight loading and the frictional forces onthe rim ledge due to rim movement. These “normal imperfections” includesuch things as eccentricity of the rotor in the stator, unbalancedmagnetic pull, and the elastic deformation of the rotor and stator. Thiscauses the push-pull frictional forces noted above to increase infrequency from once or (a few times) per start-stop cycle to once ortwice per revolution, a clearly different fatigue regime in whichmillions of cycles occur relatively quickly. As an example, supposethese machines⋅ were started and stopped once per day; then 365cycles/year would occur. But if they were operated even 12 hours/day at277 rpm, 457 million cycles would occur in 1 year.

It is impossible to avoid these forces to some degree in any hydrogenerator. Some manufacturers attempt to prevent the cracking byshrinking the rim onto the spider, so that the rim does not slide on therim ledge. On these machines, without a specific preload target, it canonly be stated that the combination of measures did not prevent themovement. It is also noted that, as these are frictional forces due tosliding, the forces on the rim ledge due to startup and shutdown are ofthe same magnitude as high cycle forces that cause smaller movements.

The following patents, patent applications, patent publications, andother documents, except of the exceptions indicated herein, are herebyincorporated by reference as if set forth in their entirety hereinexcept for the exceptions indicated herein, as follows: “The Use ofSilver in Self-Lubricating Coatings for Extreme Temperatures” by HaroldE. Sliney, prepared for the Annual Meeting of the American Society ofLubrication Engineers, Las Vegas, Nev., May 6-9, 1985; U.S. Pat. No.8,333,006, having the title “Method for removing a crack in anelectromechanical rotor”, issued on Dec. 18, 2012; U.S. Pat. No.7,866,020, having the title “Method for repairing a crack in anelectromechanical rotor, method for preventing crack growth in the same,electromechanical rotor and rotary electrical machine”, issued on Jan.11, 2011; U.S. Pat. No. 4,636,675, having the title “Rotor spider forrotary electric machine”, issued on Jan. 13, 1987; U.S. Pat. No.4,327,303, having the title “Rotor assembly for a dynamoelectricmachine”, issued on Apr. 27, 1982; U.S. Pat. No. 4,283,648, having thetitle “Synchronous electric machine with salient poles in the rotor”,issued on Aug. 11, 1981; U.S. Pat. No. 4,182,966, having the title“Ventilation system for dynamoelectric machines”, issued on Jan. 8,1980; U.S. Pat. No. 4,160,180, having the title “ROTOR LAMINATIONSUPPORT FOR VERTICAL HYDRO-GENERATOR”, issued on Jul. 3, 1979; U.S. Pat.No. 4,110,652, having the title “Mounting assembly for laminated rotorrim of dynamoelectric generator rotatable about inclined shaft”, issuedon Aug. 29, 1978; U.S. Pat. No. 3,529,193, having the title “ROTOR FORELECTRIC MACHINE WITH VERTICAL SHAFT”, issued on Sep. 15, 1970; U.S.Pat. No. 3,470,404, having the title “ROTORS FOR ROTATING ELECTRICMACHINES”, issued on Sep. 30, 1969; U.S. Pat. No. 3,112,420, having thetitle “Rotor construction for waterwheel driven electrical generator”,issued on Nov. 26, 1963; U.S. Pat. No. 3,046,426, having the title“Rotor spider for electrical machines”, issued on Jul. 24, 1962; U.S.Pat. No. 2,994,793, having the title “Dynamoelectric machine”, issued onAug. 1, 1962; U.S. Pat. No. 1,817,054, having title “Large, high speedrotor”, issued on Aug. 4, 1931; Japanese patent document number60-102829; and Japanese patent document number 54102501.

The components disclosed in the patents, patent applications, patentpublications, and other documents disclosed or incorporated by referenceherein, may possibly be used in possible embodiments of the presentinvention, as well as equivalents thereof.

The purpose of the statements about the technical field is generally toenable the Patent and Trademark Office and the public to determinequickly, from a cursory inspection, the nature of this patentapplication. The description of the technical field is believed, at thetime of the filing of this patent application, to adequately describethe technical field of this patent application. However, the descriptionof the technical field may not be completely applicable to the claims asoriginally filed in this patent application, as amended duringprosecution of this patent application; and as ultimately allowed in anypatent issuing from this patent application. Therefore, any statementsmade relating to the technical field are not intended to limit theclaims in any manner and should not be interpreted as limiting theclaims in any manner.

The appended drawings in their entirety, including all dimensions,proportions and/or shapes in at least one exemplification of theinvention, are accurate and are hereby included by reference into thisspecification.

The background information is believed, at the time of the filing ofthis patent application, to adequately provide background informationfor this patent application. However, the background information may notbe completely applicable to the claims as originally filed in thispatent application, as amended during prosecution of this patentapplication, and as ultimately allowed in any patent issuing from thispatent application. Therefore, any statements made relating to thebackground information are not intended to limit the claims in anymanner and should not be interpreted as limiting the claims in anymanner.

7.-26. (canceled)
 27. A method of repairing a hydroelectric generator structure, without removing a generator rotor, with an apparatus connected to a hydroelectric turbine structure, said hydroelectric generator structure comprising a forebay and dam, a penstock, a turbine shaft, a generator rotor assembly coupled to an upper portion of said turbine shaft, a turbine blade assembly coupled to a lower portion of said turbine shaft, a turbine chamber having a cylindrical configuration and formed by a vertically disposed turbine liner wall adjacent distal ends of said turbine blades, and a tailwater and afterbay, said method comprising: said forebay comprising a body of water at the top held by said dam at the top of the structure containing said turbine; said penstock comprising a pipe structure which carries the water from said forebay to said turbine; said tailwater comprising the area where the water is emptied after proceeding through said penstock and said turbine; said afterbay comprising the body of water where said tailwater travels; said generator rotor assembly comprising a spider attached to said turbine shaft; said spider comprising a welded steel structure having spider arms, and said spider arms having vertical posts to support a rim; said rim comprising a number of poles that provide energizing during generation of electricity; said rotor deteriorating during years of use and producing a lack of support for said rim due to operational forces; said operational forces comprising low cycle forces that occur at least with the start and stop of the generator or from transient operating conditions; said transient operating conditions comprising at least one of radial expansion of said rim from rotation of said rim, stopping and cooling of the rim upon at least one of said generator shut down, overspeed condition, out-of-phase synchronizations, short circuits, and transient torque spikes; damaging said rim and said rotor structure resulting from at least one of fretting and galling due to lack of support of said rim; said fretting comprising corrosion damage to contact surfaces under load due to operation of said generator; said galling comprising wear caused by adhesion and friction in which a transfer of material between metallic materials occurs during horizontal motion transverse to said rim; searching for and discovering damage to said rim and said rotor structure through at least one of testing via ultrasonic testing or penetrant testing; said discovery comprising testing by ultrasonic means using a transducer that vibrates at an ultrasonic frequency, and said vibrations creating echo signals that indicate the presence of a defect, testing by penetrant means using a penetrant on a non-porous material, said penetrant reveling any defects; rotating said turbine blades and said turbine shaft to facilitate repair of pitting and general deterioration of surfaces of said rim; said repair prolonging the life of said surfaces and structure of said rim by a minimum of five years; supporting mounting of said rim and energizing means to said spider and said spider arms; said supporting comprising attaching thrust plates to the top of said rim to provide support for said rim from above, so that said rim is held up from said thrust plates; said thrust plates comprising machined plates attached to the top of said rim, adjacent to said spider arms, using a number of bolts and screws; said bolts comprising at least commercial Grade 5 bolts; threading of said bolts into the top plate of said rim; allowing for tightening said bolts of said thrust plate to said rim as said thrust plate wears over time;
 28. A method for repairing a loss of support of a rim of a rotor during operation of an electrical generator, the rotor of the electrical generator being disposed for rotation about a vertical axis, the rotor comprising a shaft extending along the vertical axis, a spider attached to the shaft and extending radially away from the shaft, the spider having vertically spaced apart top and bottom sides with respect to the direction of gravity, the rim carrying poles and surrounding the spider, the weight of the rim normally being totally or partially supported on ledges disposed on the spider during normal operation of the electric generator, the loss of support of the rim being caused by mechanical failure or loss of at least a portion of the ledges, the method comprising the step of: (a) supporting at least a portion of the rim against the top side of the spider and thereby relieving some or all of the weight of the rim being supported by the ledges without the need to repair any of the failed or lost portions of the ledges.
 29. The method for repairing of claim 27 wherein the rim comprises vertically spaced apart top and bottom sides with respect to the direction of gravity, and step (a) comprises the step of: (b) fastening at least one support member on the top side of the rim, each at least one support member extending away from the rim and over the top side of the spider, the at least one support member transferring at least a portion of the weight of the rim to the spider.
 30. The method for repairing of claim 29 wherein the at least one support member comprises a plurality of thrust plates and step (b) comprises the step of: (c) fastening the plurality of thrust plates to the top side of the rim, the plurality of thrust plates being spaced part from one another and extending over the top side of the spider.
 31. The method for repairing of claim 30 further comprising the step of: (d) disposing a wear plate between each of the plurality of thrust plates and the top side of the spider.
 32. The method for repairing of claim 30 comprising the step of: (d) fastening each thrust plate of the plurality of thrust plates by one or more screws extending through the thrust plate and being screwed into the top side of the rim.
 33. The method for repairing of claim 29 wherein the rim comprises a plurality of rim studs or rim bolts extending upwardly from the top side of the rim, and step (b) comprises the step of: (c) fastening each at least one support member to a respective set of at least one rim stud or rim bolt of the plurality of rim studs or rim bolts.
 34. The method for repairing of claim 33 wherein the plurality of rim studs or rim bolts are threaded rim studs or threaded rim bolts, and step (c) comprises the step of: (d) threading a fastener onto each at least one rim stud or rim bolt of each respective set.
 35. The method for repairing of claim 29 wherein the spider comprises a plurality of spider legs extending from the shaft to the rim, and the at least one support member comprises a plurality of support members, wherein step (b) comprises the step of: (c) disposing each of the plurality of support members adjacent a respective spider arm and extending over the top side of each respective spider arm.
 36. The method for repairing of claim 35 wherein each spider leg of the plurality of spider legs comprises a vertical post having top and bottom sides disposed on the top and bottom sides of the spider respectively, the ledges being disposed on the vertical posts, the at least one support member comprises a plurality of support members, and step (c) comprises the step of: (d) disposing each support member of the plurality of support members adjacent to a respective vertical post of the plurality of spider legs, each support member extending over the top side of the respective vertical post.
 37. The method for repairing of claim 29 wherein the rim comprises a plurality of rim studs or rim bolts extending upwardly from the top side of the rim, the spider comprises a plurality of spider legs extending between the shaft and the rim, and each at least one support member comprises a plurality of support members, wherein step (b) comprises the step of: (c) disposing the plurality of thrust plates on the top side of the rim adjacent to a respective spider arm, each thrust plate of the plurality of thrust plates extending over a top side of the respective spider arm; (d) disposing a wear plate between each of the plurality of thrust plates and the top side of the respective spider arm; and (e) fastening each thrust plate of the plurality of thrust plates to the top side of the rim by fastening the thrust plate to a set of two or more rim studs or rim bolts with sleeve bolts.
 38. The method for repairing of claim 28 wherein the rim and the spider cooperatively define an interference fit therebetween while the rotor is at a standstill while performing step (a), the interference fit generating a frictional force resisting vertical movement of the rim with respect to the spider.
 39. The method for repairing of claim 28 wherein prior to performing step (a), the rim floats with respect to the spider during normal operation of the electric generator.
 40. The method for repairing of claim 28 wherein the rim is lifted off the ledges after completing step (a).
 41. A method for repairing a loss of support of a rim of a rotor of an electrical generator of a vertical hydrogenerator, the rotor of the electrical generator being disposed for rotation about a vertical axis when driven by a turbine of the hydrogenerator, the rotor comprising a shaft extending along the vertical axis, a plurality of spider legs attached to the shaft and extending radially away from the shaft, each of the spider legs having vertically spaced apart top and bottom sides with respect to the direction of gravity and a ledge, the rim surrounding the spider legs, the rim comprising vertically spaced apart top and bottom sides with respect to the direction of gravity, the weight of the rim normally being totally or partially supported on the ledges of the spider arms during normal operation of the hydrogenerator, the loss of support of the rim during operation of the hydrogenerator being caused by mechanical failure or loss of at least a portion of the ledges, the method comprising the steps of: (a) fastening a plurality of plates to the top side of the rim, each plate of the plurality of plates being placed adjacent to a respective spider leg and extending over the top side of the respective spider leg, each thrust plate transferring at least a portion of the weight of the rim to the respective spider leg.
 42. The method for repairing of claim 41 wherein the rim surrounds the spider legs while performing step (a) and wherein the rim comprises an end plate disposed on the top side of the rim, and step (a) comprises the step of: (b) fastening the plurality of plates to the end plate of the rim.
 43. The method for repairing of claim 41 wherein each spider leg comprises a vertical post adjacent the rim, and each ledge is machined into a respective vertical post.
 44. The method for repairing of claim 41 wherein the ledges no longer support the rim after performing step (a).
 45. The method for repairing of claim 41 wherein the rim comprises rim studs or rim bolts extending upwardly from the top side of the rim, and step (a) comprises the step of: (b) fastening each plate of the plurality of plates to a respective set of one or more of the rim studs or rim bolts, wherein each set of the one or more rim studs or rim bolts supports a portion of the weight of the rim.
 46. The method for repairing of claim 45 comprising the steps of: (c) disposing a sacrificial plate between each spider leg and the plate adjacent to the spider leg; (d) fastening each plate of the plurality of plates to the respective set of one or more rim studs or rim bolts by fasteners that receive the rim studs or rim bolts and are tightened to urge the plate against the top side of the rim; and (e) periodically re-tightening the fasteners to compensate for wear of the sacrificial plates caused by subsequent operation of the hydrogenerator after performing step (d). 